Method and device for activation of a detonator

ABSTRACT

A method is described for detonation of a blasting charge in a fluid environment and which is placed inside a hollow body, such as in an ignition pellet. The method is characterised in that an ignition pellet is used, which is arranged to be deformed under the influence of a number of alterations or pulsations between high and low pressure in the surrounding fluid environment, with the detonation triggering unit inside the body being activated at the subsequent contact with the fluid environment as a consequence of the pellet being deformed. In rupturing, external fluid at overpressure is released into the cylinder and drives a firing pin against a detonating cartridge. A device for an ignition pellet is also described.

The present invention relates to a method and a device for detonation ofa blasting charge in a fluid environment, and where the blasting chargeis positioned inside a hollow body, such as in an ignition pellet, aswill appear from the preamble to the following claim 1. Further, theinvention also relates to an application.

More precisely the invention relates to an ignition device of anignition mechanism which is applied together with explosives inliquid-filled pipes and well holes. It is arranged for remote operationfor detonating of explosives, for example in order to perforate a pipewall or to perforate or remove plugs in oil and gas wells. Theproduction from the reservoir may then commence.

For different appliances, triggering explosive charges is previouslyknown, and is based on release by mechanical means or by using anelectrical primer with a cable connection.

Remote controlled ignition pellets, which are based on the use ofpressure increases via a liquid inside a pipe or a well bore are knownfrom U.S. Pat. Nos. 5,680,905, 5,632,348 and 4,886,127. A rupture discor the like inside the pipe is made to break so that the pressure mayexert a force onto a firing pin which in turn is moved to initiate thedetonation of a detonating cartridge inside the pellet.

It is an object of the invention to provide a completely new method tobring about the detonation of such ignition pellets/mechanisms as afurther development of the previously known solutions.

It is a further object of the invention to provide a completely newstructure of such an ignition pellet, so that it may be remotelyoperated by means of the new triggering mechanism.

The method according to the present invention is identified by thefeatures appearing in the characteristic clause of the following claim1. The preferred embodiments appear in the dependent claims 2-7.

The device according to the present invention is identified by thefeatures appearing in the characteristic clause of the independent claim8. The preferred embodiments appear in the dependent claims 9-16.

Compared with the state of the art, the ignition charge (blastingcharge) may be triggered to detonate by means of a sequence of pressureoscillations, which can be exerted from the liquid inside the pipe or inthe well from the exit side, such as from the surface.

According to the invention the ignition pellet is used for perforating apipe wall or for perforating or removing plugs in oil and gas wells,thus, for example, for starting the production from a reservoir througha pipe.

The feature distinguishing the present invention from previously knowntechnology, is its unique way of functioning which, without affectingthe reliability, makes it possible to be made from materials whichevaporate or dissolve due to the detonation pressure, so that theproduction of liquid/crude oil through the pipe may start directly.According to the invention, these properties can be obtained by theignition pellet or the ignition mechanism being structured as a cylindercomprising a completely leak proof low pressure chamber. In a well-knownmanner, a pressure operated firing pin is arranged inside the lowpressure chamber, associated with an ignition cartridge. In the solidmaterial of the cylinder one or more scores, grooves or recesses aremade, which create a plurality of deformation or attenuating areas ofthe solid material of the cylinder. The ignition cylinder is positioned,such as by its end section, in relation to the object (for example aglass plug) to which the detonation pellet shall exert its detonationforce.

The other end of the cylinder can be kept in tension by means of aspring, which will counteract that external pressure will compress thecylinder by way of destruction of the attenuating areas of the solidmaterial of the cylinder, something that may cause the detonation chargeto explode unintentionally. When an outer/external increasing fluidpressure is exerted on the cylinder, this will be axially compressed anddeformed in the recesses/attenuating areas when the axial force exceedsthe stiffness of the solid material of the cylinder and the tension ofthe spring.

When the pressure is released/eased, the cylinder, helped by the spring,will return to it original length. Thereby, a crack will immediatelypenetrate inwards in the cylinder, in connection to the deformed crackinitiation or score in the solid material as a consequence of thematerial fatigue or the attenuation of the solid material of thecylinder. After a number of pressure swings, the crack will finallyreach through the solid wall material of the cylinder so that theexternal fluid pressure penetrates into the cylinder and will then drivethe firing pin which is originally held in place with the help of ashear pin or the like, into the detonation cartridge/blasting chargewhich then will detonate. The metal in the cylinder will consequentlyreach its yield point and a high pressure will thereby contribute to thedeformation. The spring, which is fastened on the outside of thecylinder, ensures that the cylinder is stretched out again when thepressure is eased. Such forward and back movements will therebyreinforce a fatigue rupture in the attenuated area.

Alternatively, the mentioned spring can be fitted internally at the oneend of the cylinder. The spring is then better protected. Besides, thespring shall only contribute by creating such movements in the solidmaterial of the cylinder so that fatigue of the solid material isachieved.

This simple construction and mode of action permits the use of materialswith low evaporation and combustion temperatures so that afterdetonation, a minimum of components from the ignition device and itsmechanism remain. The ignition pellet is made from a metal, preferablyaluminium or zinc, or alloys of these.

The invention shall now be explained further in connection with thefollowing figures, in which:

FIG. 1 shows an ignition pellet according to the invention with aninternal chamber, a firing pin and a detonation cartridge/blastingcharge.

FIG. 2 shows a plug, such as a glass plug, which is fitted for pressuretesting of a pipe where the ignition pellet in the device according tothe invention has an object to detonate an explosive charge andpulverise the plug when the test is completed.

The pellet/cylinder is shown in FIG. 1 with the reference number 10. Thepellet 10 comprises an internal drilled hole or hollow space 10 a inwhich the ignition mechanism itself is placed, equipped with a firingpin 13 and a blasting charge 14, with the blasting charge 14 positionedat the bottom of the drilled hole in the one end of the cylinder. Thereis atmospheric pressure or an under-pressure of gas/air in the hollowspace 10 a. This will result in the pressure variations, as aconsequence of movements of the cylinder wall, being absorbed and notbecoming sufficient to move the firing pin so that the blasting chargeis detonated.

The firing pin 13 can be suspended inside the hollow space with a shearpin, or the like. When the ignition pellet ruptures, the high pressurecontributes to push the firing pin in towards the lower pressure aroundthe blasting charge. The lower spike 30 of the firing pin 13 penetratesinto the blasting charge and triggers the detonation. The ignitionpellet is made from a metal, preferably aluminium or zinc, of alloysthereof, or from corresponding metals. This end of the pellet 10 thatencompasses the blasting charge is positioned adjoining the object, suchas a glass plug 17, which the blasting charge is to act against.

The other end of the pellet 10 comprises an enlarged, circular,flange-like section 20 which forms a hook 22. In the cylindrical pelletbody, a score, indentation or crack initiation 11 is cut in the solidmaterial of the cylinder wall. A spring 12 is fastened with anappropriate initial tension between the underside of the hook 22 and anupwardly turning edge 24 on the outer cylinder wall which is formed bythe indentation 11. The spring will thereby counteract an eventual axialcompression of the pellet/cylinder 10 caused by an externaloverpressure.

According to the invention, a number of mutually separated scores orindentations can be cut in the solid pellet material around the pelletcircumference, but it has been found that two such cut scores which aremutually spaced apart result in good deformation characteristics for thepellet.

According to the invention, when the solid wall material has a thicknessof about 4-5 mm, an attenuation groove or furrow in the solid materialcan be 2-3 mm deep and with a V-shaped cross section as shown in thefigure. But one shall not be limited to this.

According to an alternative solution for the ignition device accordingto the invention, the detonation can be started when the blasting chargecomes into contact with liquid that flows in through the opening in thecylinder when the solid material of the pellet wall is ruptured.

The indentation 11 is thereby lying between the two mounting points onthe spring 12 on the cylinder. With pulsating alternations between highand low pressure, the metal in the cylinder will reach its yield pointand the metal will alternatively be compressed by the counter-effect ofthe spring 12 and stretched (bending/compressing/stretching) by theco-operating effect of the spring, respectively. Finally, when the solidmetal material reaches its yield point at the indentation, a deformationof the cylinder wall arises. Thereby, the high pressure gets access tothe hollow space in the cylinder and the firing pin breaks the shear pinand is pushed into the low-pressure chamber and makes contact with theblasting charge. Such high temperatures arise during the blasting thatthe metal (aluminium/zinc) evaporates.

FIG. 2 shows a plug 17, such as a plug made of glass, which sits in apipe 18 as a soluble or removable seal against flow of fluid through thepipe for carrying out tests. The cylindrical ignition device 10according to the invention is placed down in a hole 26 in the plug 17with the explosive blasting charge 14 lying against the plug surface inthe bottom of the hollow/hole.

When the plug has carried out its function and shall be removed,pressure variations are applied through the fluid, which fills the pipeor bore hole, such that the pressure variations exert a variablepressure/force on the ignition pellet so that a fatigue/fatigue fracturearises which in turn opens the pellet and sets off the blasting charge.

The pressure tight cylinder is filled with a gas with atmosphericpressure or lower pressure so that the pressure variations as aconsequence of the movements in the cylinder wall itself are absorbedand not sufficient to drive the firing pin and start the detonation.

1. Method for detonation of a blasting charge in a fluid environment,and which is placed inside a hollow body, such as in an ignition pellet,characterised in that an ignition pellet is used which is arranged to bedeformed under the influence of a number of alternating or pulsatinghigh and low pressures in the surrounding fluid environment, with adetonation triggering unit inside the body being activated under thesubsequent contact with the fluid environment as a consequence of thepellet being deformed.
 2. Method according to claim 1, characterised inthat the detonation triggering unit comprises a firing pin which isbrought to abut a blasting charge and explode this under the influenceof an overpressure from the fluid environment.
 3. Method according toclaims 1-2, characterised in that a blasting charge is applied which istriggered when it comes into contact with the liquid from the fluidenvironment.
 4. Method according to claims 1-3, characterised in thatthe metal in the ignition pellet is compressed and stretched,respectively, to bring about a fatigue fracture or the like in the solidmaterial (from a metal) of the ignition pellet which thereby opens foraccess to the detonation triggering unit.
 5. Method according to one ofthe preceding claims, characterised in that the compression andstretching, respectively, are carried out by the counter-effect andco-operating effect, respectively, of a spring in connection to theignition pellet.
 6. Method according to one of the preceding claims,characterised in that the deformation resulting from the pressure pulsesis concentrated to an area of the pellet in that a groove is cut intothe solid metal material, in said area a gradually larger crack throughthe solid material of the wall is provided and which finally gives thefluid access to the hollow space of the ignition pellet.
 7. Methodaccording to one of the preceding claims, characterised in that theignition pellet is made of metal, such as aluminium, or copper, oralloys thereof.
 8. Device for an ignition pellet comprising a blastingcharge placed inside a hollow part of the ignition pellet and anappliance which initiates detonation of the blasting charge on contactwith a surrounding fluid environment, characterised in that an area ofthe solid wall material of the ignition pellet comprises means whichpromotes deformations in the mentioned area when the pellet is subjectedto pressure influences from the fluid environment.
 9. Device accordingto claim 8, characterised in that the deformation promoting meanscomprises grooves or scores which are cut into the solid material of thewall.
 10. Device according to one of the claims 8-9, characterised inthat a spring is fixed onto the pellet so that the mentioned means inthe form of grooves or scores lies between the fixing points for thespring onto the pellet.
 11. Device according to one of the claims 8-10,characterised in that the spring is arranged to promote the deformationsby stretching the ignition pellet after a preceding deformingcompression, thereby to provide a fatigue failure or the like in theignition pellet solid material which thereby opens for access to thedetonation triggering unit.
 12. Device according to one of the precedingclaims 8-11, characterised in that the detonation triggering unitcomprises a firing pin arranged to collide with the blasting charge andexplode this.
 13. Device according to one of the preceding claims 8-12,characterised in that the blasting charge is arranged to be triggeredwhen it comes into contact with liquid from the fluid environment 14.Device according to one of the preceding claims 8-13, characterised inthat the hollow space in the ignition pellet that holds the blastingcharge is filled with gas at atmospheric or lower pressure so that thepressure variations as a consequence of movements in the cylinder wallare absorbed and do not become sufficient to drive the firing pin. 15.Device according to one of the preceding claims 8-14, characterised inthat the deformation resulting from the pressure pulsations isconcentrated to an area of the pellet in that a score is cut into themetal, in said area a gradually larger crack through the solid materialof the wall is provided, and which finally gives the fluid access to thehollow space of the ignition pellet.
 16. Device according to one of thepreceding claims 8-15, characterised in that the ignition pellet is madefrom a metal, such as aluminium or copper, or alloys thereof. 17.Application of an ignition pellet according to the preceding claims toperforate a pipe wall or to perforate or remove plugs in oil and gaswells, thereby to start production from the reservoir through the pipe.